This invention concerns a screen lining for a screening machine whose screen frame has parallel supporting sections running in the direction of conveyance of the screened material, with plate-shaped screen elements made of plastic that form the screen surface and have locking devices at least on the sides facing the supporting sections with which they can be locked on strips having corresponding locking devices, which strips in turn have locking devices on the lower side for detachable connection to the supporting sections.
Screen linings of the aforementioned type are used for classifying granular materials such as construction materials, ores and so forth. The replaceable screen elements made of plastic such as castable polyurethane used for this purpose are characterized by good wear resistance to hard materials for screening that cause wear and on the other hand are characterized by their good elasticity which makes it possible to join the screen elements to the supporting sections and/or each other by means of relatively simple locking devices and with the additional advantage that they can be installed manually by means of a simple hammer without any other mounting devices and can also be lifted up and replaced manually by means of simple lever tools.
The known screen linings differ essentially only in the method of assembly and the structural devices needed for this purpose. For example, the screen elements are designed so they are flat on the facing ends and are provided with bolts that project downward and have a semicircular cross section (German Patent 2,437,809), whereby the semicircular bolts of neighboring screen elements complete each other to form a complete bolt and are engaged in suitably shaped holes on the supporting section of the screen frame. The bolts also form locking devices through an appropriate design on their periphery by means of which they engage in the holes on the supporting section to lock them. In assembly, the screen elements are positioned in such a way that the partial bolts which supplement each other to form a complete locking bolt can be driven from the top into the holes in the supporting section.
In another known embodiment (British Patent 1,228,454) the screen elements have holes into which pushbutton-like bolts are driven as locking devices so their top side rests on the screen element and they engage in appropriate recesses in the supporting section with a thickened end at the other end. With a similar system, cup-shaped recesses are provided on the facing ends of the screen elements and supplement each other with neighboring screen elements to form a type of borehole and they continue on the lower side in appropriate semicircular sleeves which have a back cut on the outside as a locking device. By driving a bolt of a matching shape into the cupshaped recesses that supplement each other to form a borehole, the projecting semicircular sleeves are forced outward so they reach behind the open edge of the recess in the day supporting section. At the same time the bolt with a thickened end engages behind the free end of the sleeves in the manner of a lock. The bolt with its head sits in a type of blind hole and thus presses the neighboring screen elements onto the supporting section (German Patent 2,632,511) .
In addition, screen linings are also known (German Utility Patent 7,838,335), whereby the supporting section is a U-shaped section that is open at the top and its legs are spread at the free edges to form a rib-shaped bulge which thus forms back cuts on the inside and outside. The screen elements which are blunted with their flat end faces have ribs with grooves whose cross section corresponds to the cross section of the legs of the U section on the lower side so that neighboring screen elements can each be driven separately onto a leg of the U section and engage it from above.
Finally, it is also known (World Patent WO 90/05594) that mounting bolts made of plastic can be inserted into recesses in the supporting section, where these bolts are designed as spreading bolts on the end that engages in the recess and also have peripheral projections at some distance above the supporting belt, for example, a peripheral bead. The screen elements are provided with cup-shaped recesses on the facing ends, where these recesses in turn have indentations that correspond to the bead and supplement each other to form a closed hole-like contour on neighboring screen elements. The screen elements are driven with their recesses from above over the mounting bolts until the bead catches in the indentation and the screen element rests on the supporting section.
Furthermore, it is also known that with flat screen surfaces (German Utility Patent 9,109,466) cupshaped indentations that supplement each other to form a hole at the abutment of the screen elements can be provided on the facing sides of the screen elements. The cupshaped indentations are provided with a back cut in the form of a peripheral groove. A strip which has locking devices on its underneath side for locking onto the supporting section and has locking bolts on the top side arranged at the same distance is driven onto the screen elements and serves to provide the attachment to the supporting section. This design has the advantage that similar screen elements can be connected to any supporting sections by means of the strip which can have any desired locking devices on its lower side.
All known screen linings--only a few designs of which have been illustrated above--have their own supporting sections which have special recesses on the top side, while the screen elements in turn have corresponding locking devices. As a result these screen linings are not compatible--in other words, screen elements of one manufacturer cannot be mounted on an existing infrastructure with certain supporting sections from another manufacturer. Another important disadvantage of these screen linings is that a stepshaped arrangement of screen elements in the direction of conveyance, which is especially desirable when working with wet materials for screening that have a tendency to cake, cannot be-produced. Stair-step screen linings where the individual screen elements are inclined with an increasing slope in the direction of conveyance therefore require special screen elements which in turn cannot be used with flat screen surfaces. Thus it is known (World Patent WO 89/08509) that the screen element can be provided with ribs that project downward on the opposite ends in the direction of conveyance, in which case the rib that is toward the front in the direction of conveyance sits loosely on the flat infrastructure of the screen frame, and the rear rib in the direction of conveyance is locked onto a supporting section, so the individual screen element on this end rests at a higher level than on the front end in the direction of conveyance, which thus gives it its slope. The rear end in the direction of conveyance projects over the supporting section in the direction of conveyance and also reaches over the front end of the next screen element, forming a type of stair-step effect. These screen elements with different profiled ribs on opposite ends and with a specially shaped profile of the rib to be locked onto the supporting section consequently have an asymmetrical design and can be mounted only on special infrastructures. Furthermore, no flat screen surface can be produced from these screen elements.